| 摘要 |
PURPOSE:To prevent local fatigue of a timing belt by shifting in the peripheral direction at least one of space sides of an engaging starting end portion out of a normal position in the case where all spaces are formed in equal pitches to lessen contact force between the space and the belt. CONSTITUTION:When a space 12 in turning angle ranges A-C having a large driving torque reaches an engaging terminal end portion, torque for lifting an intake and exhaust valve is increased to increase tension of a timing belt 10. Since the side of each space 12 of a cam sprocket 9 is formed in such a manner as to shift in the turning direction from a normal position, an engaging portion between the timing belt 10 and the cam sprocket 9 is elastically deformed depending upon tension applied to that portion, so that the pulling force of the timing belt 10 for the sprocket 9 is substantially equally disposed in a contact portion between the side of each space 12 and the toothed surface of the timing belt 10. |
